1. Field of the Invention
The present invention relates in general to furnace burners, and in particular to a new and useful spin vane for fossil fuel-fired burners.
2. Description of the Related Art
Among the key physical features of burners used in industrial and utility boilers are the spin vanes which typically are located in at least one annular secondary air flow passage that surrounds the burner fuel nozzle. These spin vanes function to change the flow direction of incoming secondary (combustion) air and to impart a swirl velocity on the air as it exits the burner and mixes with the burning fuel. The imparted swirl velocity changes the air-fuel mixing characteristics of the burner and by so doing affects the emission production level and unburnt carbon losses of the combustion process. The spin vanes usually are fabricated from flat sheet metal, and they may be situated in the annular air flow passage(s) so that they are either stationary or movable in relation to the incoming air. Where the spin vanes are movable, they often may be adjusted from a completely closed position to a fully opened position. Movable spin vanes can be useful in instances where field tuning a burner is needed to meet certain performance requirements specified by a burner user.
Spin vanes may be used in both single and dual register burners. FIG. 1 illustrates a known single register burner 10 of The Babcock & Wilcox Company (B&W) with spin vanes 11 located in annular secondary air flow passage 12 which surrounds burner nozzle 13. Pulverized coal and primary air, which serves principally as a coal transport medium, are supplied to burner 10 at inlet 14. Secondary air is delivered to annular secondary air flow passage 12 from windbox 15 which is positioned concentrically about passage 12. Secondary air flow from windbox 15 to passage 12 can be controlled by sliding air damper 16. Burner nozzle 13 and passage 12 respectively deliver the pulverized coal/primary air mixture and the secondary air to the interior of furnace 17 through opening 18 in furnace wall 19. As indicated in FIG. 1, spin vanes 11 induce a swirled air flow pattern which is directed into a burner flame.
FIG. 2 depicts a known dual register burner 20, also of B&W. Like the single register burner 10, the dual register burner 20 has a burner nozzle 13, a pulverized coal/primary air inlet 14 and a sliding damper 16. Dual register-burner 20 is distinguishable from single register burner 10 by inner secondary air zone 22 and outer secondary air zone 24, both of which air zones encircle burner nozzle 13 and thereby serve as passages through which secondary air is delivered to the interior of furnace 17. Secondary air zones 22 and 24 are separated from one another by air separation plate 25 which is positioned concentrically about burner nozzle 13. Inner secondary air zone 22 and outer secondary air zone 24 have movable spin vanes 26. Outer secondary air zone 24 also has stationary spin vanes 28 located upstream of movable vanes 26 situated in the outer air zone. As indicated in FIG. 2, inner and outer secondary air mixing patterns respectively exit from inner secondary air zone 22 and outer secondary air zone 24 and are directed into a burner flame.
For further clarity, FIG. 3 shows an enlarged profile view of the known spin vanes 11 and 26 which have been pointed out respectively in FIG. 1 and FIG. 2, above. As shown in FIG. 3, the plate-like spin vane is defined by base edge 31, leading edge 32 which intersects one end of base edge 31 at obtuse angle A, trailing edge 33 which intersects the other end of base edge 31, also at obtuse angle A, and curved outer edge 34 which intercepts the ends of leading and trailing edges 32 and 33, which are farthest from base edge 31.
U.S. Pat. No. 1,620,180 discloses angled vanes with a projecting flange. The flange, however, is not placed in a flow path and is fixed to the vane for support purposes, and not for air flow direction.
U.S. Pat. No. 2,647,568 discloses vanes or ribs which are inclined relative to the burner's axis. While the vanes or ribs have flared and contoured surfaces, they do not have any extension perpendicular to part of the length.
U.S. Pat. No. 2,515,813 is a further example of angled vanes without an extension.
U.S. Pat. No. 3,049,055 discusses optimum vane angularity.